1. Field of the Invention
The present invention relates to an endoscopic system having a fog prevention function of an observation window in an insertion portion of an endoscope.
2. Description of the Related Art
In general, an observation window disposed at the distal end of an insertion portion of an endoscope is at a temperature equal to an outside ambient temperature of, for example, approximately 25° C. before being inserted into a lumen that is an observation target. The environment inside the lumen is at a temperature of approximately 37° C. and at a humidity of nearly 100%. Thus, if moisture in the lumen adheres to the surface of a lens and generates fog or waterdrops thereupon due to a temperature difference between the temperature of the lens of the observation window and the temperature inside the lumen at the time of insertion, an observation image becomes difficult to view. For example, a configuration known as a technique for removing the fog injects a cleaning fluid from an injection hole disposed in the vicinity of the observation window to remove the fog. However, the observation window again fogs up if its temperature is low.
Thus, for example, Jpn. Pat. Appln. KOKAI Publication No. 2006-282 suggests a configuration in which a heater serving as a heat source is disposed in the vicinity of an objective optical system serving as an observation window to prevent or remove the fog on the observation window. In Patent Literature 1, a temperature sensor for controlling the temperature of the heater is disposed in the distal end of an insertion portion in the vicinity of the heater, in addition to an electric power supply wire laid for supplying electricity to the heater, and a communication wire laid for acquiring temperature information.
As disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2006-282 described above, feedback control that uses the temperature sensor is normally performed for the temperature control of the heater. Therefore, if the observation window fogs up when inserted in the lumen, the heater is heated on the basis of the temperature detected by the temperature sensor so that the fog on the observation window can be removed. When there is a large temperature difference between the temperature of the lens of the observation window and the temperature inside the lumen, the heater is heated in advance for temperature adjustment to raise the temperature of the observation window before insertion so that the temperature may be substantially the same as the temperature of an observation target.